Methods and devices for controlling a drive unit are already known, in which a setpoint value for an output variable of the drive unit is limited in such a way that an overrun fuel cutoff of the drive unit is prevented. If the driver of a vehicle releases the accelerator pedal at an engine speed that is greater than the idling speed, then he normally desires a deceleration of the vehicle by the drag torque of the engine including the operation of ancillary components of the vehicle. For the transition from an acceleration condition to an overrun condition of the vehicle, a setpoint value for the engine torque is filtered so that the vehicle is not decelerated too abruptly and no abrupt load reversal ensues. In this manner, a load reversal damping is implemented. Normally, what is to be achieved thereby is that following the filtering all cylinders of the internal combustion engine of the vehicle are cut off.
The cutoff in this instance, however, is enabled only after a torque threshold value has been reached near or equal to the zero torque if the engine speed still exceeds the predefined idling speed by more than a predefined threshold value. This cylinder cutoff is also known as an overrun fuel cutoff. Often a cutoff of the cylinders is not possible for reasons that do not depend on the formation of the threshold value for the engine torque, for example in order to ensure a tank ventilation or a sufficient catalytic converter temperature or if the engine speed is close to the idling setpoint speed.
For filtering the setpoint value of the engine torque, in this case a minimum torque greater than zero is predefined as the target value, which lies in the range of the drag torque. This is to prevent the output torque of the filter from falling below a clutch zero torque at all or from falling below a clutch zero torque at an excessively steep time gradient. The clutch zero torque is in this instance equal to a torque loss.
This approach is problematic in that the behavior of the vehicle during a load reversal, i.e. during the transition from the acceleration condition into the overrun condition is not reproducible since the distance of the minimum torque from the clutch zero torque differs as a function of the clutch zero torque or of the torque loss.